Some online dictionaries (like LEO) offer audio files of words and some phrases. ATIP Proser Speech Sythesis is used by LEO, and by going to their website, you can also create audio files of whole sentences or short paragraphs. The pitch and speed of the various voices (three German, two American, one Turkish, one French) can be customised.

Some Australian speakers have an ingrained habit of having a rising intonation at the end of sentences. If transferred to a language like German, this has the effect of making them sound unsure of what they have said, or constantly in need of affirmation by the listener, as a rising intonation is more generally a marker of questions. I think that listening to a synthesised sentence with different voices and pitches could help students to become more aware of the falling intonation that is preferable at the end of sentences in German.

While not yet a true substitute for a native speaker, the technology behind synthesised audio files is improving, and this makes them useful for checking the pronunciation of unfamiliar words.

A much more frivolous (but fun) use is to put in a long tongue-twister. Challenge yourself or your students to beat the synthesised voice on "extreme fast"!